Chill hours

tstrum

Mame
Messages
121
Reaction score
43
Location
Oklahoma
USDA Zone
7a
when trying to calculate or gage chill hours for trees, is it continuous hours below 45F or any hour below counts? We’ve been having nights in the low 30s but up in the low 60s during the day. Do those hours at night count towards chill hours or does it have to stay below for it to count?
 

Bonsai Nut

Nuttier than your average Nut
Messages
12,420
Reaction score
27,871
Location
Charlotte area, North Carolina
USDA Zone
8a
They do not have to be continuous.

For my stone fruits, we generally have a "cold degree days" requirement that needs to be met for them to fruit. We are always warm during the day, so it is the cold at night that matters.
 

miker

Chumono
Messages
726
Reaction score
688
Location
Wyomissing, PA
USDA Zone
6b
I have read somewhere that some chill hour calculation systems actually subtract for temperatures 60F and above. In my opinion, this is not an accurate way to calculate the hours. Look at the vast areas of deciduous forests in areas like, for example, the Florida Panhandle. If hours above 60F counted as negative toward the total, there would be few to no chill hours except during the coldest winters, and therefore, one would think that the vast number of temperate species growing there would fail to thrive/survive.

There are some chill hour calculators online, but I prefer to just calculate for my location myself, using climate data from wunderground.com. I basically just keep track of how many hours between November 1 - March 31 that are at or below 45F. Does anybody know the scientific basis for instead only calculating hours between 32F-45F?

I could go on and on about this topic, as it is a big area of interest for me and how it relates to my horticultural interests.
 

0soyoung

Imperial Masterpiece
Messages
7,496
Reaction score
12,832
Location
Anacortes, WA (AHS heat zone 1)
USDA Zone
8b
when trying to calculate or gage chill hours for trees, is it continuous hours below 45F or any hour below counts? We’ve been having nights in the low 30s but up in the low 60s during the day. Do those hours at night count towards chill hours or does it have to stay below for it to count?
Just the accumulation, as @Bonsai Nut said.
Twenty minutes below 40F, then 2 weeks at 70F, say, is still twenty minutes of chill time. It is as though plants have some 'dormant stuff' that only gets destroyed by time below 40F.

The plant stays dormant until all the 'dormant stuff' is gone AND temperature goes above 40F. Trouble arises for many people because the chilling requirement is satisfied, temps rise, buds break, and a hard freeze happens - once the chill hours are had, it is impossible to keep the trees dormant once the temp rises above 40F (or so).
 

sorce

Nonsense Rascal
Messages
32,908
Reaction score
45,579
Location
Berwyn, Il
USDA Zone
6.2
Just wondering what you will do with this information once you have it.....?

I ask because just reading that post is unsettling.
Seems a lot of worry about something we can't, or shouldn't, change, or try to "play God" with.

I've never done anything special for winter, mostly because I couldn't.
Until this spring I never had anything wake up early.

I messed with them and they died.
Lesson learned.

If something wakes up early.....

Just dont do anything.
Don't move it, don't repot it, don't worry about it.....

Ooooooooeeeeewww......

Forgive me but this "as the buds swell" BS.

My buds on these (Amur/Ulmus) started swelling in February....
For near 2.5 months they stayed like that through further freezes and thaws until they knew it was time to wake up, when they continued growth.

I am certain had I just left them alone they would be alive.

I am certain, seeing buds swelling, even opening a little, has caused people to move their trees into a different place, in hopes to try to "save" them..

This can work.

But fret not I say......

The tree is well equipped to know the weather.
More equipped than we are aware.

I view a setup like Judy's working.
Where everything is consistent.

My NFG system works. Cold froze don't care.

But this in-between.....

Inconsistent, garages, coldframes...etc....

Seems to make everything so much more difficult than it needs to be.

Of course........
Everyone enjoys bonsai differently.

Maybe some folks yearn to carry heavy shit and fret....

I'd rather be eating Xmas cookies!

Sorce
 
Messages
1,039
Reaction score
1,400
Location
Azores
I'm pretty sure we don't meet the chill hours required for trees over here. Yet, deciduous trees still grow here and go through their normal cycle of leaf fall etc. some only leaf out late in spring when temperatures are already much warmer than 45f. So there must be something else. Photoperiod?
 

tstrum

Mame
Messages
121
Reaction score
43
Location
Oklahoma
USDA Zone
7a
Thank you guys for the responses! This helps a lot!

@sorce - I live in Oklahoma and our weather is crazy volitile and being new to bonsai I am trying to understand better what species will do well in my area and zone hardiness has its limitations in telling me what will/won’t do well in my area. Plus (at least as I understand it) if this winter keeps being this warm, and we don’t hit chill hours and my trees have a weaker spring, I would have a better sense as to why instead of freaking out about something I did, knowing instead that it was just the weather.

As the the buds and moving trees around, I don’t do that either. I let them be throughout. But I want to be able to gage what that then means for the tree the cloning spring.

Of course, as I am fairly new, all the above may be incorrect understanding of what chill hours are and how to adjust accordingly.
 

sorce

Nonsense Rascal
Messages
32,908
Reaction score
45,579
Location
Berwyn, Il
USDA Zone
6.2
I follow.

Except for tropicals....of course....
And these situations of more delicate trees, which should be kept in the best possible consistent situation....

Winter (or lack of chill hours) alone won't kill a tree. Or effect its spring vigor.

I work almost exclusively with local dug, and local nursery material....

Simply on the ground and left alone, winter won't kill em, or even phase them.

However....repot to early, prune too late, let em dry out.....and you get death.

I consider a healthy nursery specimen at 100% health.
If you keep that health above 70%....
Winter is a non-issue.

A complete non-issue.

Confusion arises when we are not talking about the same type of trees and winter.

Newbs may hear of a white pine on its own roots being protected....
And assume their nursery Mugo is as delicate.

On the flip.....
Even the hardiest tree may not survive up here if imported from further south, until acclimated.

Note note....
Acclimation and Protection are not the same!
Acclimation Ends!

But screw acclimation!
Unless you're Grimmy!

If you can sniff it from your door.....pot it!

Sorce
 

Bonsai Nut

Nuttier than your average Nut
Messages
12,420
Reaction score
27,871
Location
Charlotte area, North Carolina
USDA Zone
8a
Just wondering what you will do with this information once you have it.....?

I don't track it, because my stone fruits are landscape trees and I can't do anything about it. If we have a warm winter, my peaches just don't flower or fruit - but they still are healthy, bud out with new growth, etc.

But even in my yard, I have microclimates. For example, right now I have bristlecone pine and several Japanese white pine cultivars that I have in bright indirect lighting on the north side of my house, in an area that stays cool quite a bit into the middle of the day. If I go out the front door of my house at 7 AM it may be 60F... while it is still 45F in the back in this sheltered area.
 

rockm

Spuds Moyogi
Messages
14,182
Reaction score
22,183
Location
Fairfax Va.
USDA Zone
7
when trying to calculate or gage chill hours for trees, is it continuous hours below 45F or any hour below counts? We’ve been having nights in the low 30s but up in the low 60s during the day. Do those hours at night count towards chill hours or does it have to stay below for it to count?
I really wouldn't worry about this. In your area, with dormant trees outside, all will have satisfied their "chill hour" requirements by spring. It's not worth the trouble calculating the total hours.
 

Dan92119

Mame
Messages
177
Reaction score
193
Location
San DIego CA
USDA Zone
10a
For my area chill hours matter. For my fruit trees they are low chill hours or I would never get any fruit. (This is for my semi dwarf trees)

I have in the past ordered hawthorn seedlings I don’t remember which kind but they did not do well here. They didn’t really loose their leaves here. So they didn’t go dormant. They ended up dying after about 3 years.

I have ordered a few crabapple seedlings this year. It will be interesting if they survive since I can’t get them locally.
 

rockm

Spuds Moyogi
Messages
14,182
Reaction score
22,183
Location
Fairfax Va.
USDA Zone
7
For my area chill hours matter. For my fruit trees they are low chill hours or I would never get any fruit. (This is for my semi dwarf trees)

I have in the past ordered hawthorn seedlings I don’t remember which kind but they did not do well here. They didn’t really loose their leaves here. So they didn’t go dormant. They ended up dying after about 3 years.

I have ordered a few crabapple seedlings this year. It will be interesting if they survive since I can’t get them locally.
Well, yeah. You're not going to have much success with trees like apple and other species that require a winter. You don't have enough of a winter to be successful with more temperate climate trees that need cold. Ordering species online that require a longer winter is iffy at best. If you want fruit trees, I'd stick with the species that are sold locally...
 
Messages
1,039
Reaction score
1,400
Location
Azores
According to this website, even though the average temperature of my coldest month is only 14 C (57F) I still get around 450 chill hours, meaning that "You can generally grow all low and medium chill fruit varieties providing low chill plants are protected from late spring frosts." That's far more chill hours than I would assume for my area...
 
Messages
1,039
Reaction score
1,400
Location
Azores
According to this website, even though the average temperature of my coldest month is only 14 C (57F) I still get around 450 chill hours, meaning that "You can generally grow all low and medium chill fruit varieties providing low chill plants are protected from late spring frosts." That's far more chill hours than I would assume for my area...

My deciduous are only starting to drop leaves now, but my Ficus are still pushing new growth. All outside.
 

Bonsai Nut

Nuttier than your average Nut
Messages
12,420
Reaction score
27,871
Location
Charlotte area, North Carolina
USDA Zone
8a
My deciduous are only starting to drop leaves now, but my Ficus are still pushing new growth. All outside.

We have had an unusually temperate / warm winter. It is forecast to be 80 today. It was in the 80's all last week, including a few days that hit 85. This is combined with 10% humidity :eek: Extremely unusual for this time of year.

Many of my deciduous trees have not gone into full dormancy. We are forecast to have highs in the 70's almost until Christmas. I can only hope it gets cold soon.
 

Bonsai Nut

Nuttier than your average Nut
Messages
12,420
Reaction score
27,871
Location
Charlotte area, North Carolina
USDA Zone
8a
It will be interesting if they survive since I can’t get them locally.

To grow apples in San Diego county you have to be at higher elevations like around Julian (hence their "apple festival" every year). If you are down low and close to the ocean it isn't going to happen.

However you CAN grow stone fruits like peaches, plums and the like - you just have to check their cold hours requirement in the nursery before you buy. The nursery should be able to help you understand how many cold hours you will get based on your location. If your lot slopes / faces the north it will make a huge difference as well. If your lot is on a slope facing the south, and isn't in a valley... it will be difficult.

And of course... there is always citrus :)
 

GrimLore

Bonsai Nut alumnus... we miss you
Messages
8,502
Reaction score
7,452
Location
South East PA
USDA Zone
6b
Even the hardiest tree may not survive up here if imported from further south, until acclimated.

Note note....
Acclimation and Protection are not the same!
Acclimation Ends!

But screw acclimation!
Unless you're Grimmy!

Important lesson I learned over the years. Now I do things quite differently with Hot Climate plants I invite to live here. Next year I will not by any plant from a hotter climate unless I can get it in early Spring here. No matter what I do purchased later the survival rate drops to 50 percent... That can be a lot of plants, and a few bucks... There are a few growers down South like TYTY that will work with me to get a tree to me on a specific date this year it was April 19th. A few bare root fruit trees and a Chinese elm that did splendid because of the timing and remain outdoors. I have Chinese elms I bought later in the season and they are protected in the shed this year only... Pain in the ass, and the only reason I am refining my timing from now on...

Grimmy
 

theone420

Shohin
Messages
442
Reaction score
480
Location
Palm Springs, CA. (USDA Zone 9b/10a)
I had a Anna Apple tree here in the desert and we got fruit every year before it got infested with some sort of boring worm that kills them from the inside out. it only needed 200 cold hrs and the golden dorsett is another option that only needs 100 cold hrs.
 
Top Bottom